SCB3.4.1

J3 (the black connector on the right) is always fitted and J5 & J6
are added.

J6 is a u.FL connector to which the clock output of the
Low-jitter-daughterboard can be connected.

J5 is used to select between the existing oscillator or the
Low-jitter-daughterboard.

Replacement of obsolete components (most notably a different NAND
flash)

Backplane (carrier board) 3.3.1

The backplane has been modified so the fans are always on (in the
original backplane 3.3 design the fans are controlled by software). This
keeps the hardware cooled in all circumstances.
Also more sturdy SFP cages have been used.

Low-jitter-daughterboard

A Low-jitter-daughterboard gives a significant improvement when it comes
to the jitter performance of the White Rabbit switch.